package test;

import java.util.Scanner;

public class FirstTaiBiNaQie {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n = sc.nextInt();
        int carculate = carculate(n);
        System.out.println(carculate);
    }
    public static int carculate(int t){
        if(t==0||t==1){
            return t;
        }else{
            return carculate(t-1)+carculate(t-2);
        }
    }
}
